This invention relates to compositions containing superabsorbing polymers based on L-aspartic acid and to process(es) for preparing such compositions.
Polysuccinimide (PSI) is prepared by thermal polycondensation of L-aspartic acid which can then be base-hydrolyzed to polyaspartate salt which has many industrial uses such as lubricant in metalworking fluids. Crosslinking PSI before or after hydrolysis renders the hydrolyzed salt superabsorbent in that it can absorb many times its weight of liquid such as water. This capability of absorbing significant quantities of fluids, including body exudates and aqueous compositions of all kinds, creates another important class of application for these polymers in products such as diapers, sanitary napkins, incontinence products, towels, tissues and the like. These superabsorbing polymers are in the prior art as typically disclosed in U.S. Pat. No. 5,461,085 (Nagatomo et al); U.S. Pat. No. 5,525,703 (Kalota) and U.S. Pat. No. 5,612,384 (Ross et al). Though articles of superabsorbing polymers derived from L-aspartic acid are recognized in this art as desirable, to date they are only disclosed in unshaped, particulate form as recovered from the hydrolysis step forming the salt. Note all the examples of the patents referenced above.
The absorbent body of many absorbent articles, such as diapers, sanitary napkins, incontinence products, etc., are normally comprised of one or more layers of cellulose fluff pulp, which may be intermixed with superabsorbent polymers. Since the superabsorbing polymers derived from L-aspartic acid to date are only disclosed in unshaped, particulate form, the problem exists of preventing migration of the superabsorbent polymer particles within the layers of pulp fibers.
In view of the noted applications, it would be highly desirable to provide biodegradable superabsorbent polymers derived from L-aspartic acid in compositions to facilitate formation into products such as diapers and the like. It would also be highly desirable to provide superabsorbent polymer compositions avoid the migration problem.
The superabsorbent compositions of the present invention provide a solution to many problems encountered with unshaped, particulate superabsorbent polymers derived from L-aspartic acid. For example, the superabsorbent compositions of the invention have the advantage of avoiding the problem of migration by being bound to the pulp fibers. The superabsorbent polymer component of the compositions of the invention are also biodegradable.